1. Field of the Invention
The invention relates to a receiving part for receiving a rod for coupling the rod to a bone anchoring element and a bone anchoring device with such a receiving part. The receiving part includes a receiving part body and a pressure element located at least partly in an accommodation space of the receiving part body. The pressure element has a flexible portion to clamp the head. The pressure element can assume in the receiving part body an insertion position in which introduction and removal of the head is permitted, a locking position in which the head is locked in the receiving part, and a pre-locking position in which the head is clamped by a pre-stress exerted by the pressure element.
2. Description of Related Art
Various designs of polyaxial bone screws, wherein the head is clamped from the side to lock the rotational position of the bone screw, are known.
U.S. Pat. No. 5,672,176 describes a bone screw with a receiving part with a conically shaped seat and a conically shaped pressure element which exerts a pressure onto the head from above and from the side. If the cone angle has a value laying within a specific range self-locking of the pressure element within the receiving part takes place which allows to preliminary lock the head within a receiving part while the rod is still movable in order to allow the adjustment of its position.
WO 2007/038350 A2 discloses an apparatus for connecting a bone anchor to a support rod, the apparatus including a connector body and a cap. The connector body has a socket for insertion, angulation and removal of a bone anchor. A sleeve is provided which is configured to fit over the connector body in a temporary position, in which the sleeve permits insertion of the bone anchor, to move to a provisional locking position, in which the sleeve permits angulation but prevents removal of the bone anchor, and to move to a locking position, in which the sleeve prevents both angulation and removal of the bone anchor.
U.S. Pat. No. 6,063,090 relates to a device used to connect a longitudinal support to a pedicle screw by an accommodating head having a channel to accommodate the longitudinal support. The pedicle screw and the accommodating head are connected via a conical collet chuck in the accommodating head and by a spherical head on the pedicle screw. The device allows engagement of the pedicle screw in the accommodating head after the pedicle screw has been inserted into the bone.
U.S. Pat. No. 6,132,432 describes a spinal implant fixation assembly including a bone fixation member such as a screw and a rod receiving seat which is operatively connected to the bone fixation element. In one embodiment a screw head receiving insert is provided, which is movable within the assembly between a locked position entrapping the screw head therein and an unlocked position, wherein the screw head enters or escapes.